Objective: To assess the reproducibility of the two markers of adrenergic drive, venous plasma norepinephrine (NE) and efferent postganglionic muscle sympathetic nerve activity (MSNA), in reflecting the sympathetic activation characterizing congestive heart failure (CHF).
Methods and measurements: In 19 CHF male normotensive patients (mean age: 53.0+/-2.1 years, NYHA classes II and III, left ventricular ejection fraction 35.9+/-2.9%), blood pressure (BP, Finapres), heart rate (EKG), plasma NE (HPLC assay) and MSNA (microneurography, peroneal nerve) were measured in two experimental sessions separated by a week interval. At each session, three NE samples were obtained and NE reproducibility between sessions was assessed by considering single NE samples or averaging 2-3 samples.
Results: While MSNA values showed a highly significant correlation between sessions (r=0.85, P<0.001), NE values based on a single blood sample evaluation did not correlate with each other (r=0.41, P=NS). NE correlation coefficients improved and achieved statistical significance when average data from 2 and 3 blood samples were examined (r=0.54 and r=0.57, P<0.02 for both).
Conclusions: In CHF, MSNA displays a better reproducibility pattern than plasma NE. The reproducibility of the NE approach, however, can be improved by performing the assay on multiple blood samples.